Locating devices for detecting objects enclosed in a medium are used for many applications in the area of manual work and interior finishing work, for example for locating electrical lines or water pipes. In addition to the concrete realization of the actual measurement function, the operation of the device is of decisive importance for the quality of the measurement results. A measurement device that is highly valuable from the point of view of technology may, in actual use in the field, achieve only a low degree of measurement success if the user operates it incorrectly, or proceeds on the basis of false assumptions when operating the device.
Among locating devices that are typically used to detect lines, pipes, metal beams, or wooden beams in walls, ceilings, and floors, it is possible to distinguish between various types of device based on the detection method used.
Thus, for example inductive devices produce a magnetic field that is disturbed by enclosed metallic objects. The magnetic field modified in this manner is measured by a detector having one or more coils, so that the position of the enclosed metallic object can be located by shifting or moving the locating device over the surface of the medium enclosing the object. A disadvantage of detectors of this type is that only metals can be detected.
A second class of locating devices, which can be described as capacitive devices, use a measurement capacitor in the measurement device to actively construct an electrical field that is disturbed by objects that are enclosed in the medium, e.g., a wall, a ceiling, or a floor. However, such a field does not penetrate very far into the medium being examined. For this reason, these devices are used primarily as stud finders, because they are capable of locating in particular wooden beams situated behind wall panels, such as for example plasterboard sheets or wooden paneling.
In addition, mains voltage detectors acquire the alternating voltage field of a mains voltage line capacitively, but passively, i.e. without producing an electrical field of their own, and are thus able to indicate the position and path of active electrical lines in walls.
More recently, high-frequency detectors use a measurement capacitor to produce an electromagnetic high-frequency field that can penetrate deeply into a medium being examined. When the detector passes over the surface of the medium being examined, internal changes in the material, such as those caused for example by an enclosed object, are acquired through a change of the dielectric constants of the measurement capacitor, and are located. In measurement devices of this type, it is not important whether the objects are made of metal, plastic, gases, or liquids, or contain these. It is sufficient for the electrical properties of the enclosed object to differ from those of the surrounding medium, such as for example a wall material.
Radar devices send out radar pulses that can be reflected back by objects hidden in a medium. By evaluating the reflected radar pulses, it is possible to gain knowledge of the objects enclosed in the medium.
Most of these classes of devices have in common that in order to achieve useful measurement results they must be calibrated, in particular when being switched on, and/or at regular intervals. During this calibration, an internal electronic balancing is usually carried out that is supposed to take place in a situation in which no object to be located is situated in the vicinity of the sensor.
Thus, for example metal-locating devices must be calibrated at a large distance from any metal in the vicinity. For this purpose, the device is typically held in the air, away from the wall to be examined. After the calibration has taken place, the device can be placed on the medium to be examined, for example a wall, a floor, or a ceiling, in order to locate hidden objects. Apart from the fact that such a calibration process is time-consuming, the calibration process itself entails a certain risk, because in the case of a wrongly performed calibration it is also possible for false positive or false negative measurement results to occur. In the worst case, damages to property or even to persons can result from such a miscalibration.
On the other hand, many capacitive locating devices are to be calibrated by a reference measurement in which the measurement device is in direct contact with a wall.